RR Lyrae variables in the dwarf spheroidal galaxy Leo I

Abstract

We report the discovery of a significant population of RR Lyrae variables in the dwarf spheroidal galaxy Leo I. Based on 40 V and 22 B images of the galaxy taken using the ESO Wide Field Imager we have identified so far 74 candidate RR Lyrae&#39;s in two CCD&#39;s hosting the main body of the galaxy. Full coverage of the light variations and pulsation periods have been obtained for 54 of them, 47 of which are Bailey {\it ab}-type RR Lyrae&#39;s (RRab&#39;s) and 7 are {\it c}-type (RRc&#39;s). The period distribution of the presently confirmed sample of RRab&#39;s peaks at P=0\fd60, with a minimum period of 0\fd54. The pulsational properties indicate for Leo I an intermediate Oosterhoff type, similar to other dwarf galaxies in the Local Group and the LMC. However, the rather long minimum period of the {\it ab}-type variables, and the significant number of RRab&#39;s with long period and large amplitude, suggest that the bulk of the old population in Leo I is more like the Oosterhoff type II globular clusters. The most straightforward interpretation is that a range in metallicity is present among the RR Lyrae&#39;s of Leo I, with a significant population of very metal-poor stars. Alternatively, these OoII variables could be more evolved. The average apparent magnitude of the RR Lyrae&#39;s across the full cycle is $<V(RR)>= 22.60 \pm 0.12$ mag, yielding a distance modulus $(m-M)_{V,0}= 22.04\pm 0.14$ mag for Leo I on the ``long&#39;&#39; distance scale.